DESCRIPTION OF THE PRIOR ART
A major drawback of cyanoacrylate compounds is their tendency to polymerize rapidly and often uncontrollably when contacted or mixed with various activating substances, especially substances that form ions in solution. Even trace quantities of such activators as organic salts, inorganic salts, metals, water, urea, oxides, etc., substantially increase the rate of cyanoacrylate polymerization. This tendency has limited the usefulness of cyanoacrylate compounds to ordinary adhesive applications. If cyanoacrylate compounds could be mixed with sufficient quantities of various activating substances without polymerizing immediately, they would be useful in a wide variety of additional applications.
The development of cyanoacrylates, such as methyl-2-cyanoacrylate, ethyl-2-cyanoacrylate, propyl-2-cyanoacrylate, 2-ethylhexyl-2-cyanoacrylate, isobutyl-2-cyanoacrylate, n-butylcyanoacrylate, hexyl-, heptyl-, and octyl-cyanoacrylate, etc., represented a major technological advance in the bonding and adhesive art.
The preparation of cyanoacrylates is well-known. It is described in such U.S. Pat. Nos. 2,467,926; 2,794,788; 2,912,454; and No. 2,926,188, the disclosures of which are incorporated by reference. The use of cyanoacrylate polymers as adhesives is described in such U.S. Pat. Nos. 2,776,232; 2,794,788; and No. 2,467,926, also incorporated by reference. The cyanoacrylate adhesives are fast-drying, high tensile-strength glues and bonding agents. Their use in bonding or joining materials together is very widespread in industry, in the household, and in special applications such as surgery (as tissue adhesives), dentistry, etc.
Various inorganic substances have been proposed as fillers or thickeners for cyanoacrylate monomer compositions. For example, U.S. Pat. No. 3,663,501 of Adams, et al. issued on May 16, 1972 discloses preparation of a dental cement containing finely divided sodium fluoride, fused silca, quartz, and alumina fillers. U.S. Pat. No. 3,607,542 of Leonard, et al. issued on Sep. 21, 1971 discloses the preparation of water-resistant cyanoacrylate paste containing insoluble inert fillers (such as various salts of calcium, titanium, zinc, tin, aluminum and iron) for use as adhesives in submerged applications and as fillings for teeth. Neither reference is concerned with the polymerization rate of cyanoacrylate adhesives or with its control.
Incorporation of acid inhibitors in cyanoacrylate compositions is known. For example, U.S. Pat. No. 4,182,823 of Schoenberg issued on Jan. 8, 1980 teaches that acid additives called "stabilizers" in the patent) including acid gases, other acids (such as acetic) or various Lewis acids (such as FeCl.sub.3, SnCl.sub.2 and BF.sub.3) inhibit polymerization of cyanoacrylate compositions. The patent warns, however, that such additives must be used with caution because strong acids "over-stabilize" the monomer and weak acids do not "stabilize" it sufficiently. Schoenberg further observes that the acids (which are said to act as anionic polymerization inhibitors) interfere with the cure of the adhesive.
U.S. Pat. No. 2,794,788 of Coover issued on Jun. 4, 1957 states that sulfur dioxide is effective as a stabilizer for cyanoacrylate monomers, that boron trifluoride and hydrogen fluoride are also effective, but that carbon dioxide is less effective.
U.S. Pat. No. 4,460,759 of Robins issued Jul. 17, 1984 discloses a two-part cyanocrylate adhesive composition. One part of this composition contains weakly acidic or weakly ionic compounds as accelerators for polymerization, particularly when these compositions are used on wood substrates. Such accelerators are said to include metal halides. The first part contains acid gases and free-radical compounds as inhibitors.
Although many of the above references recognize the need to control the rate of polymerization of cyanoacrylate adhesives, the additives they propose are inadequate as inhibitors because their inhibitory effect cannot be well-controlled.
As stated in Schoenberg, supra, too little acid inhibitor is not effective and two much can interfere with polymer cure. In addition, many acid additives cause polymer decomposition, and shorten the useful life of the cyanoacrylate polymer.
Accordingly, it is an object of the present invention to provide novel compositions useful as inhibitor-stabilizers for cyanoacrylate compounds and compositions.
Another object is to provide novel inhibiting-stabilizing compositions for cyanoacrylates that effectively delay onset and propagation of polymerization reations even in the presence of activators for such reactions.
Another object is to provide cyanoacrylate compositions that are temporarily or permanently rendered non-reactive to activating substances.
Another object of the invention is to provide cyanoacrylate compositions that are temporarily or permanently inhibited from polymerizing in which the inhibitor does not cause premature decomposition of the polymer.
Another object is to provide cyanoacrylate compositions that are temporarily or permanently inhibited from polymerizing to a controlled extent although they contain substantial amounts of substances that act as catalysts for cyanoacrylate polymerization.
Another object is to provide cyanoacrylate compositions that are electrically or thermally conductive and have such polymerization and stability characteristics or mechanical properties as make them suitable for use in the manufacture of electronic and microelectronic components.
Another object is to expand the uses to which cyanoacrylate adhesive compositions can be put by providing compositions comprising cyanoacrylate monomers that are controllably inhibited towards polymerization and at the same time yield polymers with the desired degree of cure and stability.
A further object is to prepare cyanoacrylate adhesive compositions that can be spray-coated in place using inter alia on artists' air brush.
Yet another object is to provide methods for inhibiting the polymerization of cyanoacrylate compounds and for preparing polymerization-inhibited and stabilized compositions containing cyanoacrylate compounds and activators.